Tool Steel A2
A2 tool steel is an air-hardening, medium-alloy cold work steel with a carbon content between 0.95% and 1.05%. Its composition, which includes chromium and molybdenum, provides high hardenability and allows reaching hardnesses of 63–65 HRC with air cooling in sections up to 100 mm in diameter. This behavior minimizes distortion and cracking during hardening. A2 is characterized by good wear resistance, deep hardness, and medium machinability, being suitable for applications where dimensional stability is critical.
Chemical composition
Section titled “Chemical composition”| Element | Content (%) |
|---|---|
| C | 0.95–1.05 |
| Mn | 1.00 max. |
| Si | 0.50 max. |
| Cr | 4.75–5.50 |
| Ni | 0.30 max. |
| Mo | 0.90–1.40 |
| V | 0.15–0.50 |
| Cu | 0.25 max. |
| P | 0.03 max. |
| S | 0.03 max. |
Physical properties
Section titled “Physical properties”| Property | Metric | Imperial |
|---|---|---|
| Density | 7.86 g/cm³ | 0.284 lb/in³ |
| Melting point | 1424 °C | 2595 °F |
Mechanical properties
Section titled “Mechanical properties”| Property | Condition / Temperature | Metric | Imperial |
|---|---|---|---|
| Rockwell C hardness | Air hardened (average) | 63–65 HRC | 63–65 HRC |
| Tempered at 205 °C | 60–62 HRC | 60–62 HRC | |
| Tempered at 260 °C | 59–61 HRC | 59–61 HRC | |
| Tempered at 315 °C | 58–60 HRC | 58–60 HRC | |
| Tempered at 370 °C | 57–59 HRC | 57–59 HRC | |
| Tempered at 425 °C | 57–59 HRC | 57–59 HRC | |
| Tempered at 480 °C | 57–59 HRC | 57–59 HRC | |
| Tempered at 540 °C | 56–58 HRC | 56–58 HRC | |
| Tempered at 595 °C | 50–52 HRC | 50–52 HRC | |
| Tempered at 650 °C | 42–44 HRC | 42–44 HRC | |
| Elastic modulus | — | 190–210 GPa | 27 557–30 457 ksi |
| Shear modulus | — | 78.0 GPa | 11 300 ksi |
| Bulk modulus (typical for steels) | — | 140 GPa | 20 300 ksi |
| Poisson’s ratio | — | 0.27–0.30 | 0.27–0.30 |
| Machinability (relative to carbon tool steel) | — | 65 % | 65 % |
Thermal properties
Section titled “Thermal properties”| Property | Condition | Metric |
|---|---|---|
| Coefficient of thermal expansion | 20–100 °C | 10.7 × 10⁻⁶ /°C |
Heat treatment
Section titled “Heat treatment”A2 steel is heated slowly to 788 °C (1450 °F), then raised to 954 °C (1750 °F) and held for 30–45 minutes before removing from the furnace and allowing it to cool in air. Air hardening provides a hardness of 63–65 HRC.
Tempering is performed between 177 °C (350 °F) and 538 °C (1000 °F), depending on the desired final hardness. To obtain 62 HRC, a temperature close to 177 °C is used, while 56 HRC is achieved around 538 °C.
Annealing is carried out at 857 °C (1575 °F), followed by slow furnace cooling at a maximum rate of 4 °C (40 °F) per hour.
Machining
Section titled “Machining”The machinability of A2 steel is medium, estimated at 65% relative to a reference carbon tool steel. Cold working in the annealed condition is recommended for chip-forming operations.
Welding
Section titled “Welding”A2 steel is weldable as it is an alloy steel, although there is a risk of crack formation. Three procedures are distinguished:
- Welding to harden annealed A2 steel: preheat to the austenitizing temperature, cool to ~500 °C (932 °F), weld at that temperature, cool to ~100 °C (212 °F), and use a hardfacing electrode.
- Repair welding in the hardened and tempered condition: preheat to the tempering temperature (minimum 200 °C / 392 °F), weld at that temperature, immediately reheat to the tempering temperature (max. 300 °C / 572 °F) for 3 hours, air cool to ~80 °C (176 °F), and temper again for 2 hours. Use a hardfacing electrode.
- Welding of A2 steel in the soft annealed condition: preheat between 300 °C and 500 °C (572–932 °F), weld within that range, and relieve stress immediately. Use a Cr-Mo alloy electrode for structural steels.
Forging
Section titled “Forging”Forging is performed in the range of 1093 °C to 913 °C (2000 °F to 1675 °F). Do not forge below 899 °C (1650 °F) to avoid crack formation.
Applications
Section titled “Applications”A2 steel is mainly used in dies, cutting knives (slitters), die shapes, and other tools requiring high wear resistance. It is suitable for cold work applications demanding minimal distortion after hardening, such as punches, stamping dies, and sheet metal forming tools.
Equivalent designations
Section titled “Equivalent designations”| Standard / Country | Designation |
|---|---|
| AISI / ASTM / UNS | A2 (UNS T30102) |
| EN (Europe) | X100CrMoV5 (1.2363) |
| AFNOR (France) | Z 100 CDV 5 |
| DIN (Germany) | 1.2363 |
| JIS (Japan) | SKD 12 |
| BS (United Kingdom) | BA 2 |
| SS (Sweden) | 2260 |
| Other standards | ASTM A681, SAE J437, SAE J438, FED QQ-T-570 |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum achievable hardness of A2 steel after air hardening?
Section titled “What is the maximum achievable hardness of A2 steel after air hardening?”A2 steel can achieve a hardness of 63–65 HRC in the air hardened condition.
At what temperature should A2 steel be forged?
Section titled “At what temperature should A2 steel be forged?”Forging must be performed between 1093 °C and 913 °C (2000 °F and 1675 °F), not dropping below 899 °C (1650 °F).
What is the melting temperature of A2 steel?
Section titled “What is the melting temperature of A2 steel?”The melting point of A2 steel is 1424 °C (2595 °F).
What is the coefficient of thermal expansion of A2 steel between 20 °C and 100 °C?
Section titled “What is the coefficient of thermal expansion of A2 steel between 20 °C and 100 °C?”The coefficient of thermal expansion is 10.7 × 10⁻⁶ /°C.
What is the carbon content of A2 steel?
Section titled “What is the carbon content of A2 steel?”The carbon content ranges from 0.95% to 1.05%.
What is the density of A2 steel?
Section titled “What is the density of A2 steel?”The density is 7.86 g/cm³ (0.284 lb/in³).
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=6218
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/stainless-steel-classifications-d_368.html
- steelnumber.com: https://www.steelnumber.com/en/equivalent_steel_iron_eu.php?zname_id=636